UA51648C2 - A method of chemical infiltration from the vapor phase with variable parameters of infiltration - Google Patents

Abstract

The infiltration conditions are changed between the start and the end of a chemical vapour infiltration process by varying at least one of the infiltration parameters, i.e. the dwell time of the gas phase, the pressure, the temperature, the precursor content of the gas phase, and the optional dopant content of the gas phase, whereby the infiltration conditions may be adapted to changes in the pore size of the substrate to control the microstructure of the material deposited within the substrate, and particularly to maintain a constant microstructure.

Description

Description of the invention

This invention relates to a method of chemical infiltration of material from the vapor phase into a porous substrate. 2 The field of application of the invention is manufacturing! products from a composite material consisting of a porous fibrous substrate or a preform compacted by a matrix, in particular, parts from a carbon-carbon composite material (a preform made of carbon fibers and a carbon matrix), or products from a composite material with a ceramic matrix (CMC).

Carbon-carbon composite materials and KMCM are used in various industries, which exploit their 70 thermostructural properties, that is, high mechanical properties that make it possible to create stressed structural elements, and the ability to preserve these mechanical properties up to relatively high temperatures. This is the case, for example, in the aerospace industry, in particular for thermal protection panels or engine nozzles, in the aviation industry, for example, for aircraft jet engine parts, and in the friction industry, in particular for aircraft brake discs. 12 Chemical infiltration of material into a porous substrate from the vapor phase consists in placing the substrate inside the shell and ensuring diffusion into the accessible internal pores of the gas phase substrate, containing at least one gaseous precursor of the material, while general control, in particular, of temperature and pressure inside the shell is carried out , so that a precipitate is formed from the precursor in the entire volume of the substrate. The precursor of carbon can be an alkane, alkyl, alkene, the decomposition of which creates pyrocarbon. For chemical infiltration from the vapor phase of a ceramic material, diffusion of a gas phase is carried out, which has one or more gaseous substances in its composition, which give the desired ceramic material during decomposition or as a result of a chemical reaction between them. So, for example, chemical infiltration from the vapor phase of silicon carbide (5iC) can be carried out with the help of a gas phase containing methyltrichlorosilane (MTS) in the presence of gaseous hydrogen (H"). Gaseous substances that are precursors to other ceramic materials, such as carbides, nitrides or oxides, are well known to those skilled in the art. Gee)

There are several methods of infiltration from the gas phase, in particular, isothermal-isobaric methods and isobaric methods with a temperature gradient.

In isothermal-isobaric methods, compacted substrates are maintained at the same temperature in their entire volume and at the same pressure every minute. The inconvenience of this method lies in the impossibility of achieving uniform compaction in practice. Indeed, the matrix material tends to settle mainly "Inside the pores located near the outer surface of the substrate. The gradual clogging of the surface pores leads to increasingly difficult access of the gas phase inside the material, which ultimately leads to the emergence of a compaction gradient between the surface and the middle of the material. It is possible, of course, one or more -/- times to treat the surface or clean the substrate in the process of compaction to open the surface system 35 pore again. But this requires interrupting the processes for the time necessary to remove the substrate from the sealing unit, cool it, clean it, re-introduce the substrate to the equipment and return it to the required temperature.

The method of chemical infiltration with a temperature gradient makes it possible to significantly limit the aforementioned "inconvenience" of the isothermal method. Between the inner part of the substrate, which is hotter, and the surface of the substrate, C 50 exposed to the gas phase, a temperature difference is established. In this case, the matrix material settles mainly in the inner, hotter part. By adjusting the surface temperature of the substrate so that

Since it was below the decomposition or reaction threshold of the gas phase, at least during the first part of the sealing process, it is possible to make the sealing front gradually move from the interior to the surface of the substrate as the process progresses. In a known way, the temperature gradient can be obtained by placing one or more substrates around the sensing element connected to the coil and the inductance in such a way that the inner surface of the substrate or substrates is in contact with the sensing element. A temperature gradient can also be obtained due to direct inductive coupling with the substrate during compaction, if the nature of the substrate allows it. These methods are described, for example, in the French patent application 2,711,647 and the American patent application 5,348,774. In the latter application, the heating of the substrates is carried out simultaneously due to communication with the receiving element and due to direct communication with linings as the seal front moves forward. In order to monitor the development of the compaction process, devices are provided for continuous measurement of the change in the mass of the substrates. Depending on the measured mass change, the process can be optimized, especially with respect to its duration, by influencing the sealing parameters, especially the power supplied to the inductor. By observing the change in the mass of the substrates, it is also possible to determine the end of the compaction process. Of course, the method with a temperature gradient

HF) makes it possible to obtain a less heterogeneous compaction compared to the isothermal method, but it can be used only for substrates of a special shape, in particular, annular substrates. o Whatever method of compaction is used, the microstructure of the material deposited inside the substrate depends on the conditions under which chemical infiltration from the vapor phase is carried out. In the case, for example, of pyrocarbon, 60 by changing these infiltration conditions, it is possible, in particular, to obtain pyrocarbon of different types: layered smooth, layered dark, layered rough or isotropic. The microstructure of resist carbon is an important characteristic concerning the properties of the densified substrate. Thus, in the case of products made of carbon-carbon composite material, they often try to obtain a layered roughness type microstructure, in particular, due to its ability to graphitize during heat treatment. Controlling the microstructure of the material, because what settles inside the substrate, is equally important for ceramic-type material.

In the case of isothermal methods of compaction, it was established that, despite the initial fixation of the infiltration parameters capable of producing a precipitate of the desired microstructure, this latter could change during the compaction process. The difficulty of maintaining a uniform microstructure was observed especially when compacting thick substrates, such as fibrous blanks with a thickness of more than 5 cm.

The same difficulty also exists in sealing methods with a temperature gradient, which is created either by inductive coupling with the receiving element in contact with the substrates, or by direct inductive coupling with the substrates.

The present invention aims to eliminate this inconvenience and to propose a method of chemical infiltration from the vapor 7/0 phase, which allows the sealing of a porous substrate with a material with a controlled microstructure.

This goal is achieved due to the fact that, according to the invention, between the beginning and the end of the chemical infiltration process from the vapor phase, the infiltration conditions are modified by changing at least one of the infiltration parameters, including the residence time of the gas phase in the shell, pressure, temperature, precursor content in the gas phase and the content of possible impurities in the gas phase in such a way as to adapt the infiltration conditions to /5 the evolution of the substrate porometry in order to control the microstructure of the material deposited inside the substrate.

Precursor here refers to a component or components of the gas phase which, under selected operating conditions, results in the deposition of the desired material within the substrate.

In the case of deposition of pyrocarbon, as already mentioned, the precursors are, in particular, alkanes, alkyls and alkenes.

Impurity here refers to a component or components of the gas phase that provides the function of activating the deposition of 2oCarbon from the precursor under selected operating conditions. An impurity can also be a precursor. Thus, in a gas mixture containing, for example, methane and propane (both are precursors), propane plays the role of an impurity when the temperature is approximately 10007C and the pressure is approximately 1.3 kPa. Other impurities, not necessarily precursors, can be used instead of propane or with propane as activators for gases that are less reactive under the aforementioned infiltration conditions (for example, to increase the reactivity of methane gas). At higher temperatures and pressures, for example at a temperature of about 11007 and a pressure of about 6.5 kPa (50 Torr), methane acts as a precursor without the need for an impurity. and)

Porometry here refers to what characterizes the porosity of the substrate and, more specifically, the shape of the porosity. For example, it will immediately show the specialist that a highly porous substrate, but with pores that are loosely connected between the layers, can essentially present the same sealing problems as a weakly porous substrate, but with pores that are strongly connected. are connected to each other, while porometry will be considered as similar.

In technology, it is common practice to carry out chemical infiltration processes from the vapor phase with predetermined infiltration parameters from the beginning to the end of the process, regardless of the porosity of the substrate. This Ge is characteristic, in particular, for isothermal-isobaric processes. The infiltration parameters are usually chosen to obtain the desired final density, which forces compaction to continue as much as possible at the end of the process relative to the need, despite the fact that the porometry is most unfavorable for the diffusion of the gas phase into the substrate. This leads to the need choose, for example, the temperature and content of the precursor slightly overestimated, which correspond to porometry in the process of the final phase of compaction.

In temperature-gradient-type methods during compaction, there is necessarily a temperature difference between the inner zone of the substrate and the outer surfaces of the substrate, while the front of compaction gradually moves from the inside of the substrate to the surface. Meanwhile, similarly to the isothermal method, the temperature in the sealing zone is controlled and precisely maintained constant at the optimal value determined for the sealing optimum. ;" The applicant unexpectedly found that chemical infiltration from the vapor phase carried out with an increased content of the precursor throughout the infiltration process, i.e. at a much higher content than usual

Used, leads to the creation of sediment with a permanent microstructure. But, and especially in isothermal methods, then there appears, and this is not unexpected, a strong compaction gradient, while compaction of the substrate inside is much less noticeable than near the surface. This compaction gradient is all the more significant - the higher the infiltration temperature. b Or, if the controlled sediment microstructure is required according to the expected properties of the compacted substrate, for this purpose it is also quite necessary to minimize the inhomogeneity of the compaction between the center and the surface of the substrate. c Gradual adjustment of infiltration parameters during the entire compaction process depending on the change in substrate porosity meets these requirements. In addition, compared to known methods with fixed parameters, it leads to a significant gain in the total duration of compaction.

Changing the infiltration conditions, when it is desired to maintain a constant microstructure, is carried out mainly by changing at least the content of the precursor and/or impurities from the first value at the beginning of the infiltration process to

F) of the second magnitude, smaller than the first, at the end of the infiltration process. ka For the content of the main precursor and/or impurities during the process, choose the maximum possible value.

Thus, for example, in the case of isothermal compaction with pyrocarbon, by chemical infiltration from the vapor phase, starting from the gas phase containing a mixture of methane or natural gas and propane, the content of propane, which is both the main precursor and an impurity, can vary from which is preferably at least 2095, which is the largest value used at the beginning of the process, to a value preferably between 2095 and 2095, which is the smallest value used at the end of the process. The content in the gas phase is measured here in volume percent. The choice of a value greater than 3595 for the largest volume content of propane, which is used at the beginning of the process, is not of interest, since only a very small acceleration of the deposition kinetics is observed.

To maintain a constant microstructure, other parameters can be changed, while the precursor content can be constant or non-constant. This is the case with temperature and pressure. Thus, as before in the case of isothermal compaction from a gas phase containing a mixture of methane or natural gas and propane, to obtain a layered roughness type microstructure, the compaction temperature can be reduced from the first value, for example, which is at least equal to about 10207C, to a second value that is less than the first, and, for example, is approximately between 9507 and 10207"C, and this second value is chosen so that the kinetics of deposition is not very slow, while the threshold value of the deposition temperature in this example is approximately 860". As before, in the same example, the pressure may be reduced from 70 a first value, for example, one that is at least equal to 2.5 kPa, to a second value that is less than the first and, for example, is between about 0.5 kPa and 2 kPa, and then again increased to the third value, for example, more than ZkPa.

It is also possible to change the residence time of the gas phase. In the case when the introduction of the gas phase into the shell, in which the substrate is placed, and the extraction of residual gases from this shell are carried out continuously, /5 the residence time is calculated as the average gas leakage time between the access to the shell and its exit, i.e., the residence time in the hot part of the device; the residence time depends in this case on the consumption of the gas phase and the volume it can occupy in the shell (a function of temperature, pressure, volume of substrates, etc.). In the case when infiltration is carried out by a pulse method, i.e. successive cycles, each of which consists of admitting a certain amount of the gas phase into the shell and extracting residual gases by creating a 2o vacuum in the shell, the residence time is the time that elapses between the start of the intake and the start of extraction . If the residence time of the gas phase is changed during the infiltration process, this change occurs mainly in the direction of increase.

Changing one or more infiltration parameters can be done continuously during the entire infiltration process or part of it, or intermittently. high school

The infiltration process can be divided into several successive stages, separated from each other in a known way, by the cleaning operation, which, as already mentioned, consists in the implementation of surface treatment with the aim of i) removing the surface sediment in order to fully open again the access of the gas phase to the internal substrate pores. In this case, the change of infiltration parameters can be carried out in an intermittent way with the establishment of a new set of parameter values for a new compaction stage. Changing the parameters does not necessarily occur at each new stage.

It is noted, in addition, that this invention can be used with methods of chemical infiltration from - the vapor phase of various types, such as isothermal / isobaric methods and methods with a temperature gradient. Ge

It is also noted that the control of the sediment microstructure can consist not only in maintaining a homogeneous microstructure throughout the deposited matrix - This is what will be most often sought - but also in - a purposeful change of the microstructure during the compaction process. yu

Thus, if we consider, for example, the case of compaction of the type with a temperature gradient by pyrocarbon obtained from the gas phase containing a mixture of methane or natural gas and propane, then different microstructures of pyrocarbon can be successively deposited, changing the infiltration parameters. In this example, the following table shows the ranges of infiltration parameter values that are suitable for obtaining layered rough-type, layered dark-type, and layered smooth-type pyrocarbons. in sh" i oveyuty 00000080 sl a S 000000000007oyu000000svoo

F te 001110103z8)011 liso iz 50

The deposition conditions indicated in Table 1 above for pyrocarbon of layered smooth type are suitable 42) also for the case of isothermal compaction. Preservation of a smooth layered microstructure, constant throughout the sediment, may in this case require changes in one or more parameters in the specified ranges during the compaction process.

Next, for information, but not to limit the scope of the invention, examples of the implementation of the method according to the invention are given.

Example 1. The porous substrate, which is a fibrous blank made of carbon fibers, is obtained as follows.

Layers of fabric 250 mm x 250 mm of pre-oxidized polyacrylonitrile (PAN) fibers are cut and 60 are placed on top of each other, connecting them together by stitching. Stitching is carried out as the blank is created, each layer being sewn to the underlying structure, maintaining substantially the same density of stitching throughout the blank, as described in particular in French patent application 2,584,106.

The resulting billet is subjected to heat treatment to convert the pre-oxidized PAN to carbon, and then compacted by chemical infiltration, placing the billet in the reaction chamber of the furnace used for infiltration. The isothermal infiltration process is carried out in four stages. At the end of each stage, the billet is removed from the furnace to be subjected to a stripping operation, which consists in removing the pyrocarbon deposited on the surface of the billet to reopen access to its internal pores and facilitate continued compaction.

The gas phase introduced into the reaction chamber is a mixture of natural gas (mainly methane) and propane, which continuously circulates between the entrance and exit of the chamber. The residence time of the gas phase in the chamber is approximately 1s, the pressure in the chamber is maintained at a value of approximately 1.3kPa (10Torr). During each stage of the infiltration process, the temperature is kept constant, which is approximately 9807C.

The change in infiltration conditions is aimed only at the parameter, which is the content of propane (the main precursor of carbon and impurity) in the gas phase. 70 Table 2 below shows for each of the four stages of the infiltration process the duration of the stage and the content of propane in volume percent in the natural gas-propane mixture. 6

The propane content changes abruptly, going from 2090 during | stage to 690 during the MI stage.

At the end of the infiltration process, the relative increase in mass of the workpiece, that is, the ratio between the increase in Its mass and its initial mass, is equal to 22095. The study of the section made in the compacted workpiece shows a substantially homogeneous microstructure of the layered rough type up to the middle of the workpiece.

Example 2.

A blank identical to the blank of example 1 is used.

Pyrocarbon infiltration is also carried out in four stages, separated by stripping, using the gas phase, which is a mixture of natural gas and propane. The residence time of the gas phase is approximately 1s, and the pressure is approximately 1.3 kPa. Gee)

The change in infiltration conditions is aimed here at two parameters: temperature and propane content and is carried out continuously. Table 3 below shows for each of the stages | - IM infiltration process duration, temperature at the beginning of the stage, temperature at the end of the stage, propane content at the beginning of the stage and propane content at the end of the stage. It is noted that the temperature of 3o changes continuously only during stages I and II, while the propane content changes continuously only during stages I and II. The change in temperature between its largest value (10507) and its smallest value (9807) is carried out exactly linearly. Similarly, the propane content changes linearly between its largest value (2006.956) and its smallest value (1006.95). It is noted that the process is of the isothermal type, since the temperature at every moment is the same throughout the workpiece.

By the end of the infiltration process, the relative increase in mass is approximately 22095. Compaction up to the middle of the workpiece has exactly the same characteristics as those stated in example 1, but the total duration of the compaction process is clearly reduced. « then 11110101 Stage Tsotadia Shotadia (Stage M All that - duration of sodium in 16003500 4001950 with Temperature of ochat C) Lobo 1016009809в0 /Temperaturakntsiass) 101690 evo zvo

With Vmotpropanutyu 20002005 and pi sl - Example C (comparative example).

A blank identical to the blank of example 1 is used. Compaction with pyrocarbon is carried out in four stages lasting 500 hours, 500 hours, 400 hours and 400 hours, respectively, separated by cleaning. The infiltration conditions are kept unchanged throughout the infiltration process, namely, the gas phase is a mixture of natural gas and propane with a volume content of propane, because the residence time of the gas phase is approximately 1.vs, the pressure is 1.5 kPa, and the temperature is 9807S.

These parameters, as well as the duration of the infiltration stages, have optimal values, which were determined by the applicant in the implementation of the classic process of chemical infiltration from the vapor phase, i.e. with 22 constant parameters that ensure compaction similar to the compaction obtained in examples 1 and 2.

GF) The relative increase in mass is the same (22095), but the pyrocarbon microstructure is not uniform at all.

It is noted that this invention is of great benefit in industrial terms, since the total duration of compaction is reduced by 1.36 times (Example 1) and by 1.82 times (Example 2) with the same result in the degree of compaction, which gives the method that is the closest analogue, but while maintaining the same microstructure throughout the infiltration.

Example 4.

A fibrous blank in the form of a disk with a diameter of 250 mm and a thickness of 3 mm is obtained by overlapping and stitching fabric layers as described in example 1.

The workpiece is compacted with pyrocarbon by chemical infiltration from the vapor phase, starting from the gas phase, which is a mixture of natural gas and propane, at a temperature of 101572 and a pressure of 1.5 kPa.

The infiltration process is carried out in two stages! and II, separated by a sweep operation. The table below gives for each of the two stages the duration of the stage, the volume content of propane and the residence time of the gas phase. and 7 etedstadya it,

Vmsttrotnueetyu 205

Time(s) of stay 1118 10 o. go what - y y y

At the end of the infiltration process, the relative mass gain is approximately 25095, the compaction is essentially uniform, and the microstructure of the pyrocarbon, layered roughness type, is the same.

Example 5.

A blank is used, identical to the blank of example 4. Pyrocarbon infiltration is also carried out in two stages, separated by stripping, using the gas phase, which is a mixture of natural gas and propane, at a pressure of 1.5 kPa.

Table 5 below, for each of the two stages, gives the stage duration, propane volume content (constant throughout each stage), temperature values at the beginning and end (continuous variation) and residence time values at the beginning and end (continuous variation) . 20 0 etdya sty all, 7 Vmetprolanurv tyu 205

Starting temperature C), 1oBO lo3o cm 1 Temperauraknyassu oo 1015 o

Time of stay is currently 1012

Time of stay in uknc() 12/18

The total increase in mass is 25095, the pyrocarbon matrix has the same characteristics as in example so

A. "

Example 6 (comparative).

A blank identical to the blank of example 4 is used. Infiltration is carried out in two stages, separated by stripping, using the gas phase, which is a mixture of natural gas and propane. Infiltration conditions "- are kept unchanged throughout the infiltration process, namely: volume content of propane in the gas phase - 3о 695, temperature - 10157С, residence time - 1.vs, pressure - 1.5 kPa. at

The duration of each stage is 500 hours to achieve compaction with a mass gain of 25095, as in examples 4 and 5.

Examples 4 and 5 prove that the invention, giving the same microstructure of the precipitated pyrocarbon, makes it possible to significantly reduce the total C 70 duration of compaction (reduction by 1.18 times and by 2 times compared to example 6). c Example 7. c» A porous blank, which is a fibrous blank made of fibers mainly of silicon carbide (5iC), is obtained by superimposing layers of fabric with a mesh weave, the threads of which consist of fibers sold by the Japanese company Nippon Carbon under the name "Misaiyup". In order to obtain a blank with a volume content of fibers of 3595 and a thickness of mm, the fabric layers are stacked and compressed in the i-th device. - The workpiece is compacted with silicon carbide, which is obtained by chemical infiltration from the vapor phase in the reaction chamber of the infiltration furnace. The isothermal infiltration process is carried out in three stages - PI. After the end of the first stage, the workpiece is removed from the furnace to disassemble the fixture, since the 5iC "iz" 20 deposit is sufficient to ensure the compaction of the workpiece, that is, to connect the fibers to each other to a degree sufficient for the workpiece to retain its shape . This is not a method with stripping between compaction stages. The gas phase supplied to the chamber is a mixture of gaseous methyltrichlorosilane (MTS), a precursor of 5IiC, and gaseous hydrogen (H2O). The residence time of the gas phase in the chamber is approximately 10 s, the pressure in the chamber is maintained at a value of approximately 13 kPa (100 Torr).

The change in infiltration conditions is aimed only at temperature. Table b is given below for each of the stages

GF) | - Ш indicates the duration of the stage, the temperature that is kept constant during each stage, and the density of the workpiece at the end of each stage. ime) at 7 etedya|stedya t stagea povo

Temperature c) Lobo) 10301010 dense le; 23.25) 65 Example 8 (comparative).

Use a blank identical to the blank of example 7. Infiltration of 5iC is carried out in two stages | and

And: a first stage of compaction, after which the workpiece is removed from the fixture, and a second stage, during which compaction is continued until a degree of compaction exactly identical to that achieved in Example 7 is achieved.

The gas phase used and the infiltration conditions are the same as in Example 7, except the temperature is kept constant throughout the process as shown in the table below. This table also shows the duration of the stages! and Ii, total duration and resulting densities. It is stated that in order to achieve the same final degree of compaction (density 2.5), the total duration of the process is definitely much longer than the total duration in example 7, the gain in this total duration, which is obtained by changing the temperature parameter, is here 25095. 0 tadya stedyatsvokoi iv Temperature (su 10101010 tight, 16) o

Example 9.

Fibrous blanks, such as the blanks of example 4, lay the coaxial so that they remain slightly separated from each other by spacers. The blanks are placed in the reaction chamber of the infiltration furnace 720 around the receiving element, which is a graphite cylindrical block, with which they contact their inner surfaces. The receiving element is heated due to inductive connection with the induction coil, which is placed outside the chamber in such a way that a thermal gradient is established between the inner surfaces of the workpieces and their outer surfaces, which are exposed to the gas phase introduced into the furnace. The blanks are compacted with pyrocarbon using a mixture of natural gas and propane. The temperature of the workpiece surface is measured and set to the desired value by adjusting the current in the inductance coil (o), as described in the international patent application 95/11868.

The conditions of pyrocarbon infiltration are changed during the compaction process as follows (see Table 8).

Fo - 325 Sealing with pyrocarbon, layered rough type, at all points of manufactured products. at

Example 10.

Act as in example 9, but changing the pyrocarbon infiltration conditions as follows (see table 9). their 2 00 sockets are related to the prince, no; with su "

The pyrocarbon microstructure of the matrix changes as the compaction front moves from the 1 middle of the billets to their outer surfaces. In the middle of the obtained products, the pyrocarbon matrix is pure layered rough pyrocarbon, then it gradually evolves in the direction of the outer surface to pure dark layered pyrocarbon, in contact with the fibers, passing through a mixture (o) of layered rough / layered dark pyrocarbons. drive 50 "co

Claims (1)

The formula of the invention 1. A method of chemical infiltration in the vapor phase of a material into a porous base using a gas phase that contains at least one precursor of the aforementioned material in a gaseous state, which includes the steps of placing the base inside the shell, introducing the gas phase into the shell, removing residual gases from the shell, and controlling according to the infiltration conditions, which are determined by a group of parameters, which includes: the gas phase residence time between the introduction into the shell and its removal from the shell, the pressure in the shell, the temperature of the base, the content of the precursor in the gas phase and the content of a possible impurity in the gas phase, which differs by that 60o the infiltration conditions change during the infiltration process, causing changes in at least one of the specified parameters between the first value at the beginning of the infiltration process and the second value that differs from the first, and the specified residence time, if it has changed, increases from the first value to the second, and the specified temperature, in case of change, decrease from the first value to the second, the concentration, in case of change, decreases from the first value to the second and the concentration of the possible impurity, in case of change, 65 decreases from the first value to the second, and the infiltration conditions are changed in such a way as to adapt the infiltration conditions to the change in porometry substrate to control the microstructure of the material deposited inside the substrate. 2. The method according to claim 1, which differs in that the pressure, in the event of a change, decreases from the first value at the beginning of the infiltration process to the second, smaller than the first value, during the infiltration process, then increases to the third value, greater than the second, at the end infiltration process. C. The method according to claim 1 or 2, which differs in that chemical infiltration in the vapor phase is carried out while keeping the base temperature constant. 4. The method according to claim 1 or 2, which differs in that chemical infiltration in the vapor phase is carried out with the establishment of a temperature gradient inside the base. 70 5. The method according to any of claims 1-4, which differs in that the change of infiltration conditions is carried out continuously. b. The method according to any of claims 1-4, which differs in that the change in the infiltration conditions is carried out in an intermittent manner. 7. The method according to point b, which differs in that chemical infiltration in the vapor phase is carried out in several 7/5 consecutive stages, and the change or each change in the infiltration conditions is carried out at the beginning of a new stage. 8. The method according to any of claims 1-7, which is characterized by the fact that for chemical infiltration in the vapor phase of pyrolytic carbon using a gas phase containing a mixture of methane and propane, the volume percentage of propane in the gas phase is changed from , which is at least 20 95, to a value between 6 95 and 20 95. 0. и и и 0. Official Bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2002, M 12, 15.12.2002. State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. c schi 6) (ee) « (Se) «- And c) - and? 1 - (o) sh» IR e) ime) 60 b5